Manufacture of pneumatic tire casings



Aug. 8, 1933. cs. MATHER MANUFACTURE OF PNEUMATIC TIRE CASINGS OriginalFiled Feb. 2, 1928 2 Sheets-Sheet 1 1 N VEN TOR. EEUQEEL. MA THE/ 7 ATTORNE Y.

Aug. 8, 1933. G. L. MATHER MANUFACTURE OF PNEUMATIC TIRE CASINGS 2, 19282 Sheets-Sheet 2 Original Filed Feb.

INVENTOR. EBB/WEE L. MATHEQ A TTORNE Y.

barren stares rarest, series MANUFACTURE OF PNEUMATEC TIRE CASENGSGeorge L. Mather, Milwaukee, Wis, assignor to The Fish Rubber Company,Chicepee Falls, 'Mass a Corporation of Massachusetts ApplicationFebruary 2, 1928. Serial No. 251,343 Renewed December 6, 1932 6 Claims.(01. 154-10) This invention relates to a method useful in tiveflexibility as forming a part at least of the building cord tires and toa structure useful in sidewall portions of the carcass. The centralpracticing the method. portion is shown at 3 and this is characterizedby According to my invention I proceed as folits flexibility as formingthe tread and any part i 5 lows: of the sidewall structure not includedin portions 60 When assembling the materials for a tire car- 2. Mymethod is characterized. by the relative cass, I locate the bead edgessubstantially the manner in which the portions 2 and 3 are formed. sameas if the rest of the carcass structure were The purpose of building thecarcass in this parto be assembled in fiat annular form accordingticular for; will be described in detail. Such to known practice, exceptthat my bead edges detail will bring out additional and preferred fea- 5are closer together. That is to say, the bead tures of the inventionboth in regard to the portion assembly is not a feature of myinvenmethod and the building former. tion, but the assembly and shapingof the flexible In the building of cord tires of large cross-secportionsof the carcass material between the bead tion, it has been found thatflat building methods portions are features of my invention. I shape forassembling of the carcass make difficulties the carcass materialadjacent the bead edges as because when the tire carcass is built with aarched portions and as if the whole cross-section flat cross sectionthroughout its flexible portions were to be of arch form from edge toedge. These and then shaped according to known methods, arched portionsextend from each bead portion the extreme movement whichthe carcass p01-0 toward the other a sufiicient distance to locate tions need toundergo, in order to pass from the greater part of the carcass materialin a subtheir annular but fiat cross-sectional form to stantially largerannulus than that in which the their doubly curved tire form, causes anobjecbeads lie, and the greater part of the carcass mao abl degree ofrearrangement of v V terial, thus located, is shaped in fiat form out ofdividual cords so that the ultimate tire is quite 25 the central portionof my carcass material as it frequently not what is desired in balancedtire is assembled. This particular procedure and its formation. Thisfault is increased when the tire purpose will be clearer from anexplanation of p a Originally assembled by the flat building theaccompanying drawings in which, method and the tire shaped by expansionis not Fig 1 shows a cross-section of a tire building only of largecross-section but of relatively small 30 drum on which my invention maybe practiced, rim or bead diameter. This latter requirement avfinishedtire carcass section being shown on in many balloon tires causes anextreme curvathe drum; v ture of the tire walls in their final form,which Fig. 2 is a diagrammatic view showing certain increases thenecessary movements of the carfeatures of the prior art practice withrespect to cass material when shaped from the flat annulus 35 fiat drumbuilding; up to tire form. As a result it has been the usual Fig. 3 is aview similar to Fig. 2, but showing practice to build only therelatively small sizes of in contrast thereto the desired practicemadetires by the flat building method, using for the available by myinvention; larger tires the old core method involving a core .Fig. 4 isa diagrammatic view of a strip of cord on which the carcass mat rialsare assembled and :0 fabric illustrating What is termed the angle of atthe same time, shaped by spinning operations cut; and 7 to approximatelythe form of the finished tire.

Fig. 5 is a diagrammatic view of the crown According to my method Iassemble the carportion of a tire carcass illustrating what is cassmaterials preferably on my peculiarly shaped termed the finish angle ofthe cords. former so that the arch portions 2 incline up- 45 My tireformer is generally indicatedat 10 and wardly from the bead portions farenough to comprises a flat raised crown portion 11, bead space the fiator central portion of the carcass 3 receiving portions 12- and archedportions 13 outwardly from the bead diameter enough so that connectingthe portions 11 and 12. The former this flat portion can be readilyshaped as aunit is preferably made adjustableas to width as at by any ofthe known means used in the-fiat build- 50 14. The bead edges orportions of the tire caring methods and without trouble due to excessivecass are shown at 1 and they are characterized movements of the parts.It should be appreas usual by being the relatively inflexible and ciatedthat this trouble is avoided by the fact'that immovable anchor portionsof the carcass. The in building the larger sized tires, to which .myarch-shaped portions adjacent the beads are invention is particularlydirected, each ply, or shown at 2 and are characterized by theirrelapair of plies, may be only slightly expanded as it results.

is placed on the drum, and the method of expanding the whole carcass asa unit is used only for that range which experience has proved to bepracticable and suitable for the adjustment of the assembled carcassmaterial. In this respect the central portion of my relatively largecarcass is shaped with all the advantages that smaller tires are shapedwith. This central portion has its edges integral with the arch-shapedportions, which act somewhat as if they were the bead edges of my tirein the shaping operation because they do not need to move enough tocause any difficulties, having already been shaped in the assemblingoperation in anticipation of the requirement that the expansion shapingstep shall be confined primarily to a limited portion of the flexibleparts of the large carcass.

Due to the fact that the arch-shaped portions when assembled are given adouble curvature approximating the double curvature of the tireformation, it is not necessary in the final shaping for them to movemuch more than would have been the case had the whole carcass beenassembled and shaped on a'core. Due to the fact that the side portionsdo not need to be moved much with relation to the central portion, theyserve as a buffer between the flat central portion which is given theextreme shaping operation and the bead edges which anchor the carcassassembly for the shaping operation.

I have found by actual experiment that I can by my method build a tirewith much greater facility on my former than the same the ofapproximately equal quality can be built on a tire shaped core; and Ihave found that the large sized tire built according to my invention hasbetter quality than the same size built on any of the so-called fiatbuilding formers now generally in use, other things being approximatelyequal.

Following this experimentation, tires have actually been built accordingto my method in large quantity on'my particular building former, withoutencountering the difficulties above mentioned, and put into use withentirely satisfactory I believe this to be due in part at least to thefollowing procedure which is considered of advantage in the practice ofmy method: in laying up the carcass laminations I build two or moreplies of cord fabric with the angle of the cords in one plyv reversedwith respect to the angle of the cords in an adjacent ply, eachlamination being in the form of a fiat strip of predetermined length orin the form of a flat annular band formed by joining the ends of thestrip. A soprepared lamination whether in the strip or annular form istermed a pocket and the pocket diameter is the diameter of the pocketwhen in unstretched annular form. The diameter of this pocket isslightly less than the diameter of the fiat portion 11 of my buildingformer. I stretch the pocket either in strip or annular form onto thebuilding former so that its central portion contracts tightly againstthe fiat portion of the former and due to the smaller diameter of thepocket its edges or skirts fall down slightly toward the arch surfaceportions 13 of the former. The latter can be truly shaped to the formerby simple rolling or stitching operations and, as a plurality of thesepockets are assembled on the former, the beads can be tied in at theedges and the carcass shaped in unit form as shown in Fig. 1. Thecarcass material may, if desired, be wound on the building former asingle ply at a time, the pocket diameter" being the diameter of thecircle of which the unstretched ply length is the circumference.

While I prefer the arch-shaped portions 2 curved transversely of theformer, as shown, it is apparent that the curvature thereof may beincreased, or flattened out, without departing from the scope of myinvention so long as the partially shaped skirts formed between the flatcentral portion and the bead edges of the tire are of an extentsufficient to enable me to start the unit shaping operation of the flatcentral portion far enough beyond the beads to avoid causing such aninternal movement of the cords in taking ultimate tire shape that theresulting difliculties will outweigh the advantages to be gained by flatbuilding methods for tires of large cross-section.

In carrying out my method I prefer the assembly at the bead edges to bemade in the relative position shown in the drawings. This beadarrangement, briefly stated, is for the purpose of preventing anexcessive rolling action of the beads or a pivoting of the carcass aboutthe bead wires during the expansion of the tire to shape, and aims topartially substitute therefor a hinging action approximately at thepoints 4. The exact building position desirable for the beads up to thepoints 4 differs for different types of bead construction and inapplying my invention it is not necessary to depart from the bestpractice in this regard as shown by the prior art. Bead arrangements tosecure a simple hinging action have been used with the fiat buildingdrums of the prior art and it will beunderstood that my invention dealswith the flexible portions of the carcass lying above the hinge.

The broad scope of my invention and the substantial advantagescommensurate with the breadth of the invention have been clearly shownabove. My broad method and novel former further make available certainparticulars of improved tire construction which will now be described,heretofore obtainable in tires of large cross-section only by buildingthem by the core method.

As previously stated, a tire casing is formed of a plurality of pliesofcord fabric, the cords of each ply crossing the crown of the tire atan angle to the center line of the tread, the cords of alternate pliesbeing inclined in opposite directions. The plies of cord fabric are cutto the desired width from a web of cord fabric, the strips being cut onthe bias and the angle of the cut preferably being related to theangular relation of the cords at the crown of the finished tire in amanner which will be briefly discussed.

In order to secure the desired functioning of the cords in the finishedtire it is necessary that they be under a certain degree of tension atthe time the rubber which surrounds them is vulcanized, this tensionassuring the proper positioning of the cords to withstand the strainsincident to tire service. To this end either at the time of building thetire, or subsequent thereto (but prior to vulcanization) or both, thetire fabric is stretched a predetermined amount. The degree of stretchimparted may be considered as the increase in area of the fabric ply inthe finished tire over its area in an unstretched condition. is thelongitudinal stretch imparted to the fabric at the crown of the carcassof the finished tire; for our present purposes this circumferentialstretch is taken as the criterion and is measured as the per cent ofincrease in the finished crown One element or factor of this stretchcircumference over the circumference of the unstretched pocket, orlength of strip, of the unstretched fabric forming the carcass ply. Forgiven materials and tire construction it is an advantage to have the percent of circumferential stretch constant for substantially. all sizes oftires. That is to say, in building large size tires this stretch shouldbe no more or less than in building small size tires if the material isthe same. This per cent of stretch I will call 1).

Referring to Fig. 5 of the drawings which diagrammatically shows theposition of the cords at the crown of a finished tire I have designatedas a the angle at which each cord crosses the center line of the tire.Tests have demonstrated that for a given type of tire this angle ashould be the same in large size tires as in small size tires. Turningnow to Fig. 4 which shows diagrammatically the position of the cords inthe unstretched strip of cord fabric as it comes from the bias cutter, Ihave designated as c the cord angle corresponding to a in the finishedtire; Bearing in mind that the tire carcass is made up of a plurality ofplies, the cords of which are inclined in opposite directions, it willbe seen that the circumferential stretch applied to the tire carcasstends to swing'the cords toward the center line of the tire, in otherWords to get a finish angle a at the crown of the tire after imparting19 per cent of stretch we must start with a cord angle c. It is adecided advantage from a manufacturing point of view, regardless of theadvantage in the finished tire, that'c be constant for all sizes oftires since the fabric may then be cut for all sizes of tires with onesetting of the bias cutter. This results in substantial savings inhandling material under mass production methods.

In Fig. 2 I have diagrammatically illustrated the prior art drum in itsrelation to the three factors a, b, and 0, just discussed, the drumbeing indicated in sectional profile at 6. The drum has a substantiallyuniform diameter 1 which is substantially equal to the bead diameter dof the tire to be built, shoulders being provided to position the beads7 of the tire carcass 8 in the manner above referred to. At the presenttime there are seven or more sizes of tires'having the same rimdiameter, that is, seven on an 18 inch rim, seven on a 19 inch rim,eight on a 20 inch rim, etc. In Fig. 2 I have shown in dotted line twosizes of tires of bead diameter d and outside diameter e and 6 Thediameter of the pocket or ply of unstretched carcass fabric isdesignated h and obviously cannot be greater than the diameter of thedrum. It is clear from an inspection of the figure that thecircumferential stretch imparted to the fabric in bringing the crown ofthe tire to the diameter (2 will be less than in bringing it to diametere and that if the cord angle 0 of the pocket having it diameter'is keptconstant in building both tires the finish angle a at the crown of thesmall tire must differ from the finish angle a of the large tire andconversely, if thefinish angle a is kept constant the cord angles 0 mustdiffer.

This illustrates the limitation of the old drum. For a single size tireon the diameterd, for instance e the stretch from pocket diameter 77. tofinished tire diameter 'e may equal the percentage of stretch b which iscalled for by desired practice and the desired angle a can be had byproperly choosing c it may be that tires differing only slightly in sizefrom 6 may also be built on the drum 6, but it is-clear that the valueof b will increase as the size of the tire increases (and in large sizetires this increase of b attains substantial proportions), since thecircumferential stretch that is imparted to the carcass when it isexpanded is increased by the increased circumference at e? over that ate Referring to Fig. 3, I have diagrammatically illustrated how myimproved drum permits the building of any size of tire and also permitsa control of the values of a, b, and c to the end that all three may bekept constant regardless of the size of tire built. At 9 I haveindicated my drum in profile section with a tire carcass positionedthereon and in dotted line I have indicated two sizes of large tires eand 6 Due to the increased diameter 1 of my drum over that of the drumof Fig. 2, it is possible to increase the pocket diameter k to adiameter 71. or k such that the stretch b is the same in bringing 71 todiameter e or in bringing I1 to diameter e t will also be evident thatwith b constant both (land 0 can be kept constant. The required value ofh for a given size of finished outside tire diameter 6 may be derived asfollows:

Where b is the constant per cent of stretch desired. It will be notedthat when the stretch is kept constant for all the sizes that the valueof the cord angle a at the crown of the finished tire may be keptconstant and it will follow that the cord angle 0 of the unstretchedfabric will also be constant. It will be noted that while the totalstretch imparted to the bands 7L and h is constant, with a given valueof J a varying portion of the stretch b is applied when the bands h or71 are applied to the support. This portion of the stretch may bedesignatad as k and for any given values of h and e we have therelation:

,f=h (l+k) Obviously when It is equal to 0, f is equal to h. The numberof sizes of tires which may be built on a given former depends on thevalue of 70 permitted by the building conditions imposed by the tirebuilding instrumentalities used, the tire specifications and the extentto which the former may be adjusted for width. The value of k for agiven supportand given tire size may be derived from (2) and (3) Fromthe above formulae it is evident that according to my invention a drummay be made for each different size, keeping a, b, c, and is constant,or that within the limits of the mechanical adjustment of the width ofthe drum and the variation in is permitted by good practice, one drummay be used for several sizes of tires. For example, it has been foundthat for 282:4.75, 28x4.95, and 29x5.00 on a 19 inch rim a single formerof 21.647 inch diameter may be used with constant values for a, b, andc, and k varying between 2.8% and'2.0%. Larger sized tires both onsmaller and larger rim diameters have been successfully built accordingto my invention, examples being 30x6.f20 for an 18 inch rim, the crowndiameter of the building former being 22.551 inches, and a 32x83? 5 fora 20 inch rim, the crown iarneter of the building former being 24.532inches, the values of a, b, and 0 being the same in all cases.

It will thus be seen that in addition to making it possible to securethe substantial advantages of flat building methods in the building oflarge tires, my invention makes possible a nice control of the buildingfactors.

Having thus described my invention, I claim:

1. A tire building former comprising an annular member, bead locatingportions adjacent the edges thereof, side portions curving inwardly andupwardly from the bead locating portions a sufficient distance to shapethe major portion of the sidewall of the tire and a flat crown portioncon necting said curved portions, said flat portion being of lessdiameter than the final crown diameter of the tire to be built thereon.

2. A tire buil ner comprising an annular member ha ing a central latcrown portion of less diameter than the final crown diameter of the tireto built thereon and lying sufficiently above the point where theflexible portions of the carcass join the bead portions of the carcassso that the stretch imparted to the crown portion of a tire builtthereon, when the latter is expanded to tire shape, may be controlled byan adjustment in the length of the plies of unstretched carcass materialwhen placed on the building former, the portions of the formerunderlying the sidewall portion of the tire being curved inwardly andupwardly from the bead supporting portion to the flat crown portion.

3. A tire building former comprising an annular member having a centralfiat crown portion lying above the point where the flexible portions ofthe carcass join the bead portions of the carcass, the diameter of theflat crown portion of the former bearing a relation to the outside crowndiameter or" the tire to be built thereon substantially expressed by theformula wherein equals the diameter of the flat crown portion of theformer, 6 equals the outside crown diameter of the tire to be built, isequals the percentage of circumferential stretch imparted to the carcassmaterial in placing it on the former and b equals the total percentageof circumferential stretch desired to be imparted to the carcassmaterial.

4. A tire building former comprising an annular member, bead locatingportions adjacent the edges thereof, inwardly and upwardly inclinedcurved portions beginning adjacent the bead locating portions andextending a sufficient distance to form the major portions of thesidewall of the tire to approximately tire form, said curved portionsterminating in a central flat crown portion, said fiat portion being ofless diameter than the final crown diameter of the tire to be builtthereon.

5. A tire building former comprising an annular member having a centralsubstantially fiat crown portion of less diameter than the final crowndiameter of the tire to be built thereon and lyin above the point wherethe flexible portions of the carcass join the bead portions of thecarcass and inwardly and upwardly inclined curved portions connectingthe crown portion and bead portions, said curved portions being ofsufficient extent to underlie the major portions of the sidewalls of thetire and shaped to confine substantial angular movement of the cords ofthe carcass material, incident to subsequently bringing the carcass totire shape, to the substantially flat crown portion.

6. A tire building former comprising an annular member having a centralsubstantially flat crown portion lying above the point where theflexible portions of the'carcass join the bead portions of the carcassand curved portions connecting the crown portion and bead portions, saidcurved portions being shaped to confine supstantlal angular movement ofthe cords of the carcass material, incident to subsequently bringing thecarcass to tire shape, to the substantially fiat crown portion, thediameter of the flat crown portion of the former bearing a relation tothe outside crown diameter of the tire to be built thereon substantiallyexpressedby the formula GEORGE L. MATHER.

